Ordinary atmospheric pressure ionization mass spectrometry devices are configured to introduce ions generated under atmospheric pressure into vacuum and analyze the mass of the ions.
Ion sources for generating ions under atmospheric pressure are available in a variety of types, including electrospray ionization (ESI) type, atmospheric pressure chemical ionization (APCI) type, matrix-assisted laser desorption-ionization (MALDI) type, and the like. In any type, a substance that makes a noise component is produced in addition to desired ions. For example, ESI ion sources are configured to ionize a sample by applying high voltage while pouring a sample solution into a small-diameter metal capillary. For this reason, noise components, such as charged droplets and neutral droplets, are also produced at the same time as ions.
An ordinary mass spectrometry device is composed of several spaces partitioned by a pore and each space is evacuated by a vacuum pump. The spaces are increased in degree of vacuum (reduced in pressure) as it goes rearward. A first space separated from atmospheric pressure by a first pore electrode (AP1) is often evacuated by a rotary pump or the like and kept at a degree of vacuum of several hundreds of Pa or so. A second space partitioned from the first space by a second pore electrode (AP2) is provided with an ion transport unit (quadrupole electrode, electrostatic lens electrode, or the like) that converges and transmits ions. The second space is often evacuated to several Pa or so by a turbo molecular pump or the like. A third space partitioned from the second space by a third pore electrode (AP3) is provided with: an ion analysis unit (ion trap, quadrupole filter electrode, collision cell, time-of-flight mass spectrometer (TOF), or the like) for ion separation and dissociation; and a detection unit for detecting ions. The third space is often evacuated to 0.1 Pa or below by a turbo molecular pump or the like. There are also mass spectrometry devices with more than three partitioned spaces but devices including three spaces or so are in common use.
Generated ions and the like (including noise components) pass through AP1 and are introduced into a vacuum vessel. The ions thereafter pass through AP2 and are converged on the central axis at the ion transport unit. The ions thereafter pass through AP3 and are separated by mass or decomposed at the ion analysis unit. Thus, the structure of the ions can be analyzed in more detail. The ions are finally detected at the detection unit.
In most typical mass spectrometers, AP1, AP2, and AP3 are often coaxially disposed. The above-mentioned droplets other than ions are less susceptible to the electric field of the pore electrode, ion transport unit, and ion analysis unit and basically tend to travel in a straight line. For this reason, if droplets traveling in a straight line are excessively introduced, the droplets can arrive at a detector and this leads to a shortened life of the detector.
To address this problem, in the technology described in Patent Literature 1, a member having multiple holes is placed between an ion source and AP1. This member does not have a hole positioned coaxially with AP1 and the introduction of noise components from AP1 can be reduced. However, the member having the multiple holes is disposed outside AP1, and the front face and back face of the member are both placed at atmospheric pressure.
To remove droplets traveling in a straight line, the central axis of AP1 and the central axis of AP2 are made orthogonal to each other in the technology described in Patent Literature 2; and the central axis of AP1 and the central axis of AP2 are eccentrically disposed in the technology described in Patent Literature 3. However, in the equipment configurations in Patent Literature 2 and Patent Literature 3, a right-angled space between AP1 and AP2 is evacuated in a direction orthogonal to the central axis of AP2 by a vacuum exhaust pump such as a rotary pump. FIG. 1 in Patent Literature 4 illustrates an equipment configuration in which the central axis of AP1 is cranked.